Gman said:got the 4000ft figure from here http://www.rense.com/general69/calls.htm although them seem to get that from another article/publications so no proof on the accuracy of the figure.
this site seems to run a number of mobile phone test at different altitudes and records the results.
http://www.physics911.net/projectachilles.htm
that is interesting, as I said I'm no expert. The other explanation, is that everyone including the media and authorities made a lot of mistakes in the weeks fallowing the incident. Which is understandable considering the scale.
I'm off to read some conspiracy sites about the mobile phones and some sites taht disprove the conspiracy. See if I can find more. However I dont think it changes anything. You still have the WTC and pentagon planes.